How to find digits after decimal? [closed] - c++

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I want to write a program in C++ to cin a Decimal number and cout the digits after Decimal
for example 0.26547 -> 5.
I wrote this but not work correctly:
int main()
{
int i=0,b;
float a ;
cin>>a ;
while(a!=0)
{
a*=10 ;
b=a ;
a-=b ;
i+=1 ;
}
cout<<i ;
}
For example for 0.258 instead of 3, returns 20.
can one explain me what is the problem of this code ?
thank you

Answer 1

C++ permits decimal representation of floating point numbers, but as far as I know all extant implementations use binary representation. And then the idea of storing the user's decimal number specification as a floating point value, loses critical information about the decimal digits: they're simply not there any more. So to count the decimal digits in the specification, you have to store it as a string.
Pseudo-code:
input number specification as a string, e.g. using getline.
verify that it's a valid number specification, e.g. using stod.
scan for the first period from the right, call this position P.
scan for the maximum number of decimal digits from position P.

Answer 2

I am unsure why your code does not work (What compiler are you using?), but I think it might related to
b=a;
Try explicitly casting your float to an int
b = int(a);
Alternatively, you could choose not to use an int, and round a float down using the function floor by including math.h #include <math.h>
float a = 5.9f;
float b = floor(a);
a -= b;